The invention relates to a delimbing apparatus for processing elongated pieces, particularly tree trunks, according to the preamble of claim 1.
For the processing of tree trunks, a harvester head is used for the purpose of gripping an upright growing tree, to cut the tree and to fell it for processing the trunk, typically for delimbing and cutting it into pieces of fixed length. The head is normally fixed at the end of a boom assembly in a working machine, such as a harvester, which is movable on a terrain by means of wheels or a crawler. Some harvester heads are also used for manipulating the trunk during loading. The harvester head is connected to the boom assembly in an articulated manner, and it comprises the necessary actuator means, normally hydraulic cylinders and hydraulic motors, by means of which the position of the head and its different functions can be controlled. The head, which, in the following description, will also be referred to as the delimbing apparatus, also comprises means which can be swivelled in relation to a frame structure. These means include e.g. delimbing means, normally pairwise on different sides of the trunk, which comprise delimbing blades for delimbing branches while the trunk is supported and transferred through the apparatus in the longitudinal direction of the trunk. Feeding means, normally pairwise on different sides of the trunk, normally comprise a feed pulley or a feed roll which is driven by a hydraulic motor, is pressed against the trunk, and pulls it by means of friction past the delimbing blades and through the apparatus. The head also accommodates cutting means, such as a chain saw, by which the trunk is cut to a desired length by stopping the trunk and activating the sawing.
Publication U.S. Pat. No. 5,219,010 discloses a known delimbing apparatus which comprises two pairs of delimbing means and one pair of feeding means. The delimbing means and the feeding means are articulated around a substantially horizontal and vertical direction in relation to the frame structure, respectively. It is also known to couple the feeding means to the frame structure in such a way that they are articulated around a substantially horizontal axis. The delimbing blade is articulated in relation to the frame structure by means of a joint. In addition to this, the joint is affected by actuators, most typically a separate cylinder which is driven by a pressurized medium and produces a stroke, producing the necessary moment force to maintain the position and force effect of the delimbing blade. Furthermore, the pair of the means is often coupled to each other by said cylinder, but the cylinder can also be connected at its other end to the frame structure. A necessary pressurized medium circuit is used to control the pressurized medium to be supplied to the actuator means.
In a conventional hydraulic cylinder, the pressure of the pressurized medium is effective on the circular piston surface which can be increased to increase the stroke force of the cylinder and thereby also the moment to be produced with the cylinder. However, this will increase the dimensions and weight of the cylinder, wherein the placement of cylinders which are large in size and have particularly long strokes becomes problematic. Cylinders protruding from the apparatus are easily collided with obstacles and damaged. At the same time, hoses and tubes for the pressurized medium in the cylinder are easily stuck and broken. The stroke of the cylinder causes a moment in the joint; however, the moment is not constant during the whole stroke, but the force effect of the means is variable. This makes it more difficult to control particularly the pressure levels of the pressurized medium circuit.
It is an aim of the present invention to eliminate the drawbacks presented above. To achieve these aims, the delimbing apparatus according to the invention is primarily characterized in what will be presented in the characterizing part of the appended claim 1.
The central principle of the invention is to use an integrated joint which has a blade structure and is driven by a pressurized medium, for the control of the means. The surface area of the blade structure of the joint can be made larger than the surface area of the piston in the cylinder, and compared with a conventional piston, the blade structure is transverse, making a small joint possible. A particular advantage is achieved in that the moment force of the joint can be increased without increasing the pressure level and the external dimensions, because by doubling the number of the blade structures, it is also possible to double the moment force. On the other hand, the moment can also be easily increased by increasing the length of the structure in the direction of the axis of rotation of the joint.
Another advantage is that a constant torque is achieved with the joint in different rotational positions, wherein the torque is not affected by, for example, variations in the geometry of the cylinder and the connecting points of a prior art joint. Another result is that the control and optimization of pressure levels of the control circuit become easier. The joint is particularly advantageous in view of bearings, because in a joint driven by a pressurized medium, the compartments of pressurized medium can be arranged symmetrically, wherein the forces effective on different sides of the joint arm compensate for and counterbalance each other. The cylinder actuators always load the bearings unevenly.
By means of the invention, the actuators and the joint structures can be combined to make a very compact and protected structure possible. Cylinder structures can be eliminated, wherein the delimbing apparatus is also suitable for limited spaces, and breakages can be avoided. Moreover, the necessary tubes and hoses can be placed more easily to be protected by the structure. In addition to this, it is possible to use integrated structures in channellings for the pressurized medium, wherein the pressurized medium is led into a joint driven by the pressurized medium, for example, via drillings in the joint arm. Particular advantages are achieved, because the control circuit to be used for the control, including its valves, can also be integrated in the joint. If necessary, the number of joints driven by the pressurized medium can be reduced by arranging a mechanical link for the transmission of the rotational movement between the pair of the means.